Fig. 5. At 1,400F, the increases in ultimate tensile strength and elongation to failure due to pressurized solidification were less significant than they were at 1,300F.
also influencing the properties. In general, UTS and elonga- tion increased as density increased. Time-temperature data showed the application of iso-
static pressure during solidification decreased solidification time (increased the cooling rate) when the section thick- ness was 1 in. (25.4 mm) or less. Beyond the 1 in. section thickness, solidification time was approximately the same whether solidified under 1 or 10 atm. Tis is the first time solidification under pressure has been
shown to increase the casting cooling rate for a sand casting. In a similar previous study, cooling rate was determined not to have an effect, but the smallest section size examined was 1.4 in.
Future Work Needed
Data on aluminum alloys A319, A356, E357 and A206 solidi- fied under pressure are limited. To quantify the improvements in mechanical properties, castings solidified under pressure should be compared to castings that have undergone post processing to eliminate porosity. Te recent study has shown that solidification under
pressure can also increase casting cooling rates, which raises the possibility of refining the microstructure. A model that accounts for the effects of pressure on solidifi- cation should be developed in the future.
This project is supported by the AMC Castings for Improved Readiness pro- gram and sponsored by the Defense Supply Center Philadelphia, Philadelphia, Pa., the Research and Development Division of the Defense Logistics Agency, Ft. Belvoir, Va. and the American Foundry Society.
32 | MODERN CASTING March 2011
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